1. Field of the Invention
The present invention relates to a display device and a manufacturing method thereof, and more particularly to a technique which is effectively applicable to a color liquid crystal display device.
2. Description of the Related Arts
As one of display devices, there exists a color liquid crystal display device which includes a liquid crystal display panel capable of performing a color display. The color liquid crystal display device is a display device which is capable of performing a high-definition color display and, recently, has been popularly used as a liquid crystal display panel for a liquid crystal television receiver set or a PC (Personal Computer), a display for a PDA (Personal Digital Assistant), a mobile phone or the like.
The liquid crystal display panel which is used in the color liquid crystal display device (hereinafter referred to as color liquid crystal display panel) is, for example, a display panel which is constituted by sealing a liquid crystal material between a first substrate (a TFT substrate) which arranges TFT (Thin Film Transistor) elements and pixel electrodes in an array and a second substrate (a color filter substrate) which arranges color filters of R (red), G (green) and B (blue) at positions corresponding to the pixel electrodes. Here, in the color liquid crystal display panel, a display pixel of one dot is constituted of a set which is formed of a R pixel having the red color filter, a G pixel having the green color filter, and a B pixel having the blue color filter.
In manufacturing the color filter substrate, for example, first of all, a black matrix which separates the R pixels, the G pixels and the B pixels on a transparent substrate formed of a glass substrate or the like is formed. Then, the red color filter for the R pixel, the green color filter for the G pixel and the blue color filter for the B pixel are sequentially formed on the transparent substrate.
In forming the color filters, a method which performs patterning of a resist in which pigment is dispersed using a photolithography method is most popularly adopted. In this method, for example, first of all, a negative resist in which pigment is dispersed is applied to a whole surface of the transparent substrate by coating, a solvent is removed by evaporation from the resist by heating so as to dry the resist. Next, the negative resist is exposed through a photo mask which blocks light except for predetermined pixel regions. After exposure, the resist in the pixel region is cured by light and is made insoluble against a developer. Accordingly, in developing the resist using alkaline solution, only regions except for the pixel regions are developed and removed whereby a pixel pattern of the color filter is obtained. Such steps are repeatedly performed with respect to the red, green and blue color filters.
Further, there also exists a method which uses a dry film resist in place of such a coating-type resist (for example, see Japanese Patent Laid-open Hei5-173320 (document 1)). In this method, a film-like negative resist in which pigment is dispersed is adhered to a transparent substrate by thermo-compression bonding and, thereafter, the above-mentioned exposure and development are performed thus forming a pixel pattern of a color filter. This method can simplify the step for forming the resist on the transparent substrate compared to the method which coats the resist. Further, by preliminarily forming an oxygen interrupting layer on the resist of the transfer film, a curing action is accelerated thus increasing the sensitivity of the resist. On the other hand, however, the method has demerits or drawbacks such as a high material cost, and no flexibility in a delicate control of color tones by changing coated film thicknesses.
Further, recently, aiming at the reduction of a material cost and a manufacturing cost, a method which forms a pattern by supplying pigment-dispersed ink to only pixel portions such as high accuracy printing (for example, described in Japanese Laid-open No. 294930/2003 (patent document 2) and ink jet printing (for example, described in Japanese Laid-open No. 221319/2000 (patent document 3).
Corresponding to a usage or an application to which the color liquid crystal display device is applied, a demand for, for example, a temperature of white color obtained by synthesizing lights which pass through the R pixel, the G pixel and the B pixel, the color reproducibility of respective colors and the like differs. Accordingly, in manufacturing the color filter substrate, it is necessary to control color tones of filter materials used for color filters of respective pixels by taking, for example, the color temperature of white color and the color reproducibility of respective colors into consideration.
As one of methods of controlling the temperature of white color and color reproducibility of respective colors, there exists a method which changes a film thickness of the pigment-dispersed resist. However, when the film thickness is largely changed, there arises a drawback such as irregularities in coating thickness and hence, only the color-tone change at a level of fine adjustment is possible. Accordingly, when the film thickness adjustment cannot cope with the required temperature of white color or the color reproducibility of respective colors, there arises a drawback that it is necessary to prepare a new pigment-dispersed resist in which the color tone is adjusted by changing a kind of pigment and a blending ratio of pigment. Further, each time the color filter substrate which differs in the temperature of white color and the color reproducibility of respective colors is manufactured, a changeover operation of the pigment-dispersed resist becomes necessary and hence, there arises a drawback that the production efficiency is lowered. Here, these drawbacks are drawbacks which are also shared in common by pigment-dispersed ink used in the above-mentioned high-definition printing and ink jet printing.
Further, as a method for controlling the temperature of white color and the color reproducibility of respective colors, for example, there has been also known a method which changes the numerical apertures of the respective pixels consisting of the R pixel, the G pixel and the B pixel, for example. However, in adopting this method, for example, it is necessary to change a pattern of an exposure mask corresponding to numerical apertures of the respective pixels or it is necessary to change sizes of the pixel electrodes on the TFT substrate. Accordingly, there has been a drawback that it is necessary to individually prepare the above-mentioned CF substrate and the TFT substrate corresponding to the required temperature of white color and color reproducibility of the respective colors.
It is an object of the present invention to provide a technique which facilitates a control of a temperature of white color and color tones of respective colors in a color liquid crystal display device, for example.
It is another object of the present invention to provide a technique which can easily form color filters of arbitrary color tones using a same filter material.
The above-mentioned object, other objects and novel features of the present invention will become apparent from the description of this specification and attached drawings.